This is a category D study designed to test the hypothesis that intravenous administration of MiKasome will reduce the density of gram-negative bacteria in the sputum and bronchoalveolar lavage fluids in patients with cystic fibrosis who are colonized with these bacteria. The study is also designed to provide safety and pharmacokinetic data for MiKosome in cystic fibrosis patients. Aminoglycoside antibodies, such as amikacin, have been the mainstay of therapy for cystic fibrosis patients who become ill because of gram-negative bacterial pulmonary infections. This family of drugs, unfortunately, has considerable toxicity (mainly renal toxicity and hearing toxicity). Encapsulation of antibiotics in liposomes can dramatically reduce toxicity by limiting exposure in sensitive tissues such as the kidney and the ear while preserving delivery of the antibiotic to the site of infection. Preclinical studies have demonstrated that the liposome-encapsulated formulation of amikacin (MiKosome) markedly prolongs the half-life of amikacin, is relatively non-toxic in the dose range anticipated for human usage, distributes into lung tissue, and is active against Pseudomonas aeruginosa (a gram-negative bacteria often causing pulmonary infections in patients with cystic fibrosis). Patients entering this study are evaluated in the GCRC and receive infusions of the drug in the GCRC outpatient clinic. Pharmacokinetic studies involving the study of bronchoalveolar lavage fluids will be done on five patients from the study cohort. The bronchoalveolar lavage will be performed in the GCRC Research Endoscopy facility.